In order to reduce weight and increase structural strength, aircraft are increasingly using composite materials, which often are non-conductive. Aircraft also have to manage electrical currents caused by electromagnetic effects (EME) such as those caused by lightning, radio towers, and static discharge by providing conductive paths and electrical isolation where required. EME such as lightning may have large currents and high voltages capable of producing electrical arcing across exposed surfaces. In aircraft made with non-conductive composite materials, good electrical paths are required to dissipate EME energy, and good electrical isolation is required to protect sensitive equipment and fluids. Bonding and grounding requirements for aircraft electrical systems such as wing ice protection systems must also be provided for.
Aircraft leading edge structures such as slats with track arms and other aircraft structures are generally designed to have grounding paths to dissipate EME energy, for example through bearings employed in such structures. However, for normal operation, the electrical system has an electrical current return network for grounding the electrical system. It may be desirable that the electrical system conduct ground current through the current return network during normal operation and not through the aircraft structure ground paths used for EME.
As shown in FIG. 4, a conditionally non-conductive material 101 can be disposed between or coated on parts of the bearing 120 to provide electrical isolation for lower voltages for bonding and grounding purposes, while providing a conductive path for EME purposes such as conducting large voltages of lightning strikes. However, use of such conditionally non-conductive material 101 typically requires that the material be applied between bearing components that by design require freedom of relative motion. As shown in FIG. 5, after the bearing components 120 are misaligned, the coating material 101 tears leaving areas 111 uncoated and thereby terminating the electrical isolation.